Most proteins produced by eukaryotic organisms are produced as larger proproteins that are generally either less active, or entirely inactive. Many proproteins are processed in transit through the secretory pathway of the Golgi apparatus where specific proteases cleave peptide bonds at specific amino acid sequences to produce functionally mature proteins. Still other propeptides are first transported to specific regions of the cell or the cell membrane where they are cleaved at specific amino acid sequences to produce mature proteins.
Proteins first produced as larger propeptides then cleaved into more functional polypeptides include but are not limited to serum albumin, cell surface receptors, adhesion molecules, peptide hormones such as pro-insulin, neuropeptides, growth factors, and components of the clotting cascade.
One especially widespread and indispensable protease active in both the secretory pathway and on, or near the cell surface, is the endoprotease furin. Furin, is itself produced as a proprotein (SEQ ID NO. 1), cycles between the Golgi apparatus, endosomes, and cell membrane. Furin is active in both embryogenesis and in mature cells. At steady state, furin is localized principally in the trans-Golgi network (TGN)/Endosomal system. Depending upon its location in the system, furin catalyses a number of different reactions, all involving proteolytic cleavage of proproteins. For example, in the TGN/biosynthetic pathway furin cleaves a propeptide to give active pro-β nerve growth factor (pro-β-NGF). Similarly, furin cleaves propeptides thereby activating pro-bone morphogenic protein-4 (pro-BMP-4) and the “single-chain” insulin pro-hormone to form the higher activity latter-form entity.
A number of pathogens also exploit host cell furin activity to help activate proteins involved in pathology. For example host cell furin cleaves the Ebola Zaire pro-glycoprotein (pro-GP) protein as part of the virus's infectious cycle. Furin located in the host cell membrane cleaves proproteins produced by bacterial pathogens to create active forms of the bacterial proteins such as anthrax protective antigen (PA), and Clostridium septicum α-toxin. Additionally, furin in the early endosome, cleaves propeptides to produce active bacterial proteins such as diptheria toxins, shigala toxin, shigala-like toxin 1, and Pseudomonas exotoxin A. Furin processes the coat protein of Human Immunodeficiency Virus (HIV) and PA toxin produced by Bacillus anthrasis. For a more through discussion of furins and furin activity, the reader is directed to “Furin at the Cutting Edge: From Protein Traffic to Embryogenesis and Disease” Gary Thomas, Nature Reviews Molecular Cell Biology Vol. 3, October 2002 pg. 753-766, which is hereby incorporated by reference in its entirety.
In addition to the propeptides already discussed furin and other subtilins-like proteases, also cleave proproteins that produce active forms of hormones and growth factors (e.g., proactivin A, hepatocyte-growth factor), plasma proteins (albumin, factor VII, factor IX, factor X), receptors (insulin pro-receptor). Additional pathogen derived propeptides processed by furin and other subtilins-like proteases include, for example, viral proteins such as HIV-1 coat protein gp160, and influenza virus hemagglutinin as well as bacterial proteins such as diphtheria toxin, and anthrax toxin. For further discussion of the role of furins in cellular metabolism and pathology the reader is directed to the following references all of which are hereby incorporated by reference in their entirety, (Decroly et al., J. Biol. Chem. 269:12240-12247, 1994, Stieneke-Grober et al., EMBO J. 11:2407-2414, 1992, Barr, Cell 66:1-3, 1991, Wasley et al., J. Biol. Chem. 268:8458-8465, 1993, Klimpel et al., Proc. Natl. Acad. Sci. USA 89:10277-10281, 1992, Tsuneoka et al., J. Biol. Chem. 268:26461-26465, 1993, Bresnahan et al., J. Cell. Biol. 111:2851-2859, 1990, Hosaka et al., J. Biol. Chem. 266:12127-12130, 1991, Vey et al., J. Cell. Biol. 127:1829-1842, 1994.
Because of furin's importance in both cellular development and maintenance and its role in pathology, furin has become the focus of considerable study. This interest has resulted in the development of some furin inhibitors useful in the study of furin activity and in the treatment of diseases that involve furin activity. Currently available furin inhibitors include the furin propeptide itself (SEQ ID NO. 1), specific alkylating agents, a polypeptide consisting of L-arginines, and polypeptide derivatives of α1-antitrypsin. For further discussion of furin inhibitors the reader is directed to: U.S. Pat. No. 6,022,855; “Polyarginines Are Potent Furin Inhibitors” A. Cameron, J. Appel, R. A. Houghten, and I. Lindberg, The Journal of Biological Chemistry, Vol. 275, No. November 24, pg. 36741-36749; and U.S. patent application publication No. 2003/0087827, all of which are herein incorporated by reference in their entirety.
A typical Furin propeptide is described in U.S. Pat. No. 6,272,365 B1. The typical sequence representative of a human furin propeptide (SEQ ID. No. 1 submitted by K. Strausberg, et al. (gi: 15082544) is available from the National Center for Biotechnology Information (NCBI).
Other alkylating agents such as ketomethylene and octapeptidyl chloromethane derivatives are effective inhibitors of furin, unfortunately they are too toxic to be of general therapeutic value. For a further discussion of these reagents the reader is directed to see, for example, S. Jallenberger, et al., Nature 1992, pp 358-361, vol. 360, which is herein incorporated by reference in its entirety.
The α1-antitrypsin derivatives used as furin inhibitors are less toxic to eukaryotic host cells than are the currently used alkylating agents. However, α1-antitrypsin derivatives are large polypeptides, not readily taken up by cells. The most practical means of delivering α1-antitrypsin derivative furin inhibitors is by gene therapy. This delivery system includes all of the complications and risks generally associated with gene therapy.
Although the general association between specific disease states and furin activity is known, it is unlikely that all disease states associated with furin activity have been discovered. Because of the essential role furin plays in metabolism, development, and a wide variety of pathologies there is an urgent need for compounds and methods for regulating furin activity. It is one object of the invention to provide such compounds and methods.